The introduction of nicks in DNA may be accomplished using photolabile nucleotides or nucleotide surrogates, resulting in so-called "caged strand-breaks".⁽¹⁾ Various non-nucleosidic monomers have been developed for this purpose.⁽²⁾ Caged Strand-Breaker CE-Phosphoramidite is the most advanced example of this strategy, allowing complete removal of the photolabile protecting group from both phosphorylated daughter strands and the avoidance of a second step involving base treatment.^2e Further, Caged Strand-Breaker CE-Phosphoramidite II also facilitates implementation of this strategy, but gives rise to daughter strands with a phosphate group on the 5'-terminus and a hydroxyl residue on the 3'-terminus.

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1. Reviews: (a) Mayer, G.; Heckel, A. Angew. Chem. Int. Ed. 2006, 45, 4900-4921. (b) Young, D. D.; Deiters, A. Org. Biomol. Chem. 2007, 5, 999-1005. (c) Tang, X. Dmochowski, I. J. Mol. BioSyst. 2007, 3, 100-110.
2. (a) Urdea, M. S.; Horn, T. US Patent 5,258,506, Nov. 2, 1993. (b) Ordoukhanian, P.; Taylor, J.-S. J. Am. Chem. Soc. 1995, 117, 9570-9571. (c) Zhang, K.; Taylor, J.-S. J. Am. Chem. Soc. 1999, 121, 11579-11580. (d) Ordoukhanian, P.; Taylor, J.-S. Bioconj. Chem. 2000, 11, 94-103. (e) Zhang, K.; Taylor, J.-S. Biochemistry 2001, 40, 153-159. (f) Dell'Aquila, C.; Imbach, J.-L.; Rayner, B. Tetrahedron Lett. 1997, 38, 5289-5292.